The present invention relates generally to a quartz resonator supported by a pedestal and, more particularly, to the shape of the pedestal.
Recently the precision of wristwatches has advanced significantly and the precision display thereof has improved from the yearly rate to the monthly rate. To manufacture wristwatches having high precision, a composite resonator which incorporates two tuning fork type quartz resonators has been developed and in which temperature variation is theoretically compensated by utilizing the difference in peak temperatures of the frequency-temperature characteristics caused by the difference in cut angles of the two resonators. Keeping pace with the demand for such high precision, the demand for miniaturization and reduction of the thickness of the wristwatches have also benn areas which have received much attention. In view of the above requirements, it is disadvantageous to incorporate two resonators in a wristwatch. One approach to overcome this disadvantage has been the development of the AT-cut quartz resonators which attain the high precision by using a single resonator. This type, however, is disadvantageous because of its large current consumption at high frequency, its short battery life, large shape and inability to enable to reduction of the thickness of the watches.
Accordingly, the GT-cut quartz resonator having excellent frequency-temperature characteristics by using a single resonator, and which is of miniature size and capable of high productivity because it is formed by a photo-etching process, is presently drawing the much attention. Using this resonator, a quartz resonator of miniature size, of small crystal impedance (CI value) and of excellent frequency-temperature characteristics is realized by a suitable combination of the cut angle, shape and electrode arrangement. The GT-cut quartz resonator is particularly excellent with respect to the frequency-temperature characteristics, i.e., several PPM within the temperature range of -80.degree. C. to 120.degree. C. Since the frequency-temperature characteristics of the resonator are decided by the dimensional ratio of the relatively long side to the short side of the resonator, the frequency-temperature characteristics are dispersed by the dispersion of the quality of the resonator due to the limitation of the accuracy of finishing. Therefore it is necessary to adjust the frequency by depositing masses on the short sides and long sides, or eliminating the masses previously deposited on the short sides and long sides by means of a laser. (The present invention particularly illustrates the method of depositing the masses by way of example.) Hereinafter several problems attended with the frequency adjustment will be illustrated in conjunction with the drawings.
FIG. 1 shows a GT-cut quartz resonator R comprising a vibrating portion 1, bridge portions 2, vibration attenuating portions 3 which prevent the transmission of the vibration to supporting portions 4, the portions 1 to 4 comprising a one piece unitary structure. The oblique lined portion indicates an exciting electrode. The frequency-temperature characteristics of the resonator are obtained by coupling two vibrational modes in a single coupling resonator. Namely, the frequency-temperature characteristics are decided by the difference in frequency of the two modes. Particularly, the frequency-temperature characteristics of the GT-cut quartz resonator are decided by the difference between the relatively short side dimension and relatively long side dimension. The higher frequency is decided by the short side dimension H which is represented by f.sub.H and the lower frequency is decided by the long side dimension L which is represented by f.sub.L. The frequency-temperature characteristics of the GT-cut quartz resonator are decided by f.sub.H -f.sub.L =.DELTA.f.
FIG. 2 shows an example in which the GT-cut quartz resonator R shown in FIG. 1 is mounted on a pedestal 5 to adjust the value .DELTA.f. In the figure, an evaporation source E is located as if the evaporation material is evaporated from the upper direction for conveniece. Actually, however, the evaporation source E is located below the resonator and the evaporation material is evaporated from the lower direction in most cases.
In case f.sub.H is adjusted, the masses evaporated from the evaporation source E are controlled to conform to the shape of a through hole provided on a mask M and deposited at the position A.sub.1 ' or A.sub.2 ' (positioned almost at the center of the long sides). This time .DELTA.f becomes smaller since f.sub.1 little changes. As f.sub.H becomes the oscillation frequency (or basic frequency) when connected to the oscillating circuit, f.sub.H is necessary to be the exponents of 2, for example. For this f.sub.H is ordinary the exponents of 2. While any frequency is possible according to the shapes of the GT-cut quartz resonator, 1 to 2 MH.sub.z band is optimum for watches. Therefore, in the case 1 MH.sub.z band is used, the frequency is 1.048576 MH.sub.z, and in the case 2 MH.sub.z band is used, the frequency is 2.097152 MH.sub.z, and both of which are the exponents of 2. When the frequency-temperature characteristics are set at the optimum value only by adjusting f.sub.H to the reference frequency, the frequency adjustment is over. Since the frequency-temperature characteristics or .DELTA.f, however, are not always optimum, .DELTA.f is set more finely by adjusting f.sub.L. The mask M is held in place to deposit the masses B.sub.1 ' and B.sub.2 ' (positioned almost at the center of the short sides). Actually, however, the resonator shifts to the mask position provided with the holes B.sub.1 ' and B.sub.2 '. Then the masses evaporated from the evaporation source E are deposited from the evaporation source E. The frequency-temperature characteristics are thus adjusted by adjusting f.sub.H and f.sub.L to the respective reference frequencies and setting .DELTA.f at the optimum value. The figure also shows the GT-cut quartz resonator mounted on the pedestal connected to a lead terminal 7 for extracting the signal by an adhesive member such as a solder 6 or the like. The pedestal is provided to support both sides of the supporting portions 4 of the resonator to ensure the shock resistance since the bridge portions 2 are very thin to attenuate the vibration sufficiently at the vibration attenuating portions, as already illustrated in the explanation of the GT-cut quartz resonator in FIG. 1.
FIG. 3 shows an embodiment of the method of a adjusting the evaporation frequency used generally for mass production. The figure shows the conventional evaporating method in which the evaporation source is located beneath the resonator in contrast with FIG. 2. In FIG. 3, a resonator R is mounted on the pedestal 5. The resonator provided with the pedestal is connected to the lead terminal 7 provided with a plug, and connected to an oscillating circuit provided within the device to be oscillated, whereby the frequency is adjusted by measuring the frequency. A plug portion 8 comprising the resonator is pressed by a spring biased pressing rod 9 to position or fix the resonator to the device. Then a voltage is applied to the evaporation source E to evaporate the masses, whereby the masses are deposited on respective positions on the resonator by way of the through hole provided on the mask M. In this method, the evaporation source is fixed and the resonator R and the mask M are rotated as a unit, whereby only the resonator R whose frequency is to be adjusted and the mask M are positioned directly above the evaporation source.
FIG. 4 shows a plan view of FIG. 3 viewed from the X direction. The resonator R is not shown in the figure since it is mounted on the other side of the pedestal. Assuming that a resonator mounted on the pedestal is improperly aligned and is set inclined at some angle (a resonator 5B is shown by way of example), the positions to deposit the masses are shifted from the hole position of the mask M, whereby the masses can not be deposited on the desired positions on the short sides and the long sides. In actual practice such a problem often occurs. On the other hand, since the masses are deposited by oscillating the resonator, it is necessary to provide a space between the mask and the resonator to some extent, whereby the masses are deposited in a larger pattern than the actual hole shape of the mask. Moreover, the mask hole becomes smaller and gradually filled with the material as the evaporation masses are deposited therethrough repeatedly. In this way the positioning is difficult and takes a long time in the conventional frequency adjusting method by evaporation, since the resonator is held in place taking account of the mask hole. Further the shape of the masses deposited on the resonator is larger than the mask pattern due to the space existing between the resonator and the mask. Further it is necessary to periodically replace the mask when the mask hole becomes smaller.